Process for producing heavy denier regenerated cellulose filaments



Patented Aug. 17, 1954 PROCESS FOR PRODUCING HEAVY DENIER REGENERATEDCELLULOSE FILAMENTS Rudolph Woodell, Richmond, Va., assignor to E. I. duPont de Nemours and Company, Wil-.

mington, DeL,

a corporation of Delaware No Drawing. Application March 7, 1952, SerialNo. 275,454

4 Claims. (CI, 18-54) This invention relates to the production ofregenerated cellulose filaments, fibers, and the like, having apronounced crimp or curl. More particularly, it relates to an improvedmethod for producing such crimped fibers and filaments of heavy deniersat high spinning speeds.

U. S. Patent No. 2,515,834 to W. D. Nicoll discloses a process for theproduction from viscose, of crimped, wool-like fibers and filaments ofregenerated cellulose. These fibers are unique in that the crimp, afterbeing removed mechanically by stretching, combing, or the like, maybesubstantially completely restored by suspending the fiber, free from alltension, in an aqueous liquid. The process. comprises spinning filamentsinto a bath while maintaining a critical balance between thecompositions of the viscose and of the bath, imposing a high tension andstretch on the filaments during spinning, and relaxing the filaments ina liquid, free of all tension, after substantially completeregeneration. In accord ance with the first sub generic embodiment ofinvention disclosed in that patent, a viscose solution containing over5% alkali and about 7% cellulose at a salt index of 1.5-6.0 is extrudedinto a bath containing 6.59.5% sulfuric acid, 15-30% sodium sulfate, and0.l-3% zinc sulfate. The bath is maintained at a temperature of ie-75 G.The compositions of the viscose and of the bath are maintained accordingto the formula given in the patent. In addition to the above-mentionedingredients of the coagulating bath, it is permissible to have presentas much as 6% or 7% glucose or similar organic substances well known inthe art. Bath travel distances of over 50 inches are operable. Duringthe spinning of the filaments a stretch of at least 40% and a spinningtension of at least 0.5 gram per denier must be imposed. Aftersubstantially complete regeneration, the filaments are relaxed, free ofall tension, in a liquid which will swell them. The patent states thatthis treatment will result in a wool-like yarn containing above 10crimps per inch. It should be noted that spinning speedsoi only 2500inches per minute or 69.5 yards per .minute are mentioned in theexamples.

The high tension required for this process may be secured by the use ofa suitable system of guides and rollers in the bath adapted to increasetension on the filaments gradually. One illustration of rollers whichmay be employed for this purpose are rollers, provided with means fordeveloping a resistance to rotation in the bath. These are described inU. S. Patents 2,083,251, 2,083,252, and 1,878,455. Tension may also beapplied between two feed wheels during the passage of the yarn through asecondary bath, if

l caused by broken filaments and the like.

Producing heavy denier yarns of 10 deniers per filament and higher,capable of withstanding the high spinning tensions necessary in thisprocess, is very difficult. U. S. Patents No. 2,517,694 to H. D. Marionet a1. and No. 2572,9343 to M. P. Kulp et al. point out that above about10 deniers per filament, the crimping is negligible. A preference for 1to- 6 deniers per filament is mentioned in these patents Since lowerspinning tensions are necessarily imposed on the heavy denier yarn, theresultant crimp is very unsatisfactory. This difiiculty is even greaterat increased spinning speeds,-i. e., Y. P. M. and higher. Operating atincreased spinning speeds is, of course, quite desirable from aneconomic standpoint, but it is very difficult to increase these speedsand still be able to attain high spinning tensions for even the finedenier filaments without excessive breaking of filaments. causinginterruptions in the process. Attaining the required spinning tensionfor heavy denier filaments at increased spinning speeds under ordinaryconditions is a practical impossibility. The crimpability of heavydenier yarn is further reduced by the very nature of the filament. Itwould not be expected that a relatively stiff, heavy material wouldcrimp as well as a fine material.

It is an object of the present invention to produce yarn, filaments andfibers of heavy denier that are highly crimpable. A further object isthe production of heavy denier filaments and fibers, characterized byincreased breaking tensions. A further object is to provide heavy denierfilaments and fibers capable of withstanding the spinning tensionsnecessary for the production of highly crimpable yarns at increasedspinning speeds. A still further object is to provide a method by meansof which crimpable artificial fibers and filaments can be producedduring the usual course of production with a minimum disturbance tonormal production and with a minimum investment in additional equipment.Other objects will become apparent from the following description andclaims.

The above objects are accomplished in accordance with the presentinvention by spinning regenerated cellulose filaments of at least denierper filament at spinning speeds of at least 100 yards per minute, undertension, from a viscose solution into a coagulating and regeneratingbath and, after substantially completely regenerating the filaments,freely suspending the filaments, in filamentous structure form, in anaqueous liquid bath in complete absence of tension to completely relaxthem. A high degree of crimp is obtained by observing the followingcritical conditions in carrying out the process:

(a) The viscose solution must have an alkali content (calculated asNaOH) of 4.0 to 7.5%,

(b) The viscose solution must have a salt index (as determined byReinthaler-Rowe, Artificial Silk, 1928, page 69) of between 1.5 and 7,

(c) The coagulating and regenerating bath must have a sulfuric acidcontent of between 6.5% and 9.5%,

(d) The coagulating and regenerating bath must have a sodium sulfatecontent of between and (e) The coagulating and regenerating bath musthave a zinc sulfate content of between 0.1% and 3%,

(f) The filaments must travel at least 50 inches in the coagulating andregenerating bath, (9) The temperature of the coagulating bath must bebetween C. and 75 'C.,

(h) The extrusion velocity must be adjusted relative to said spinningspeed of at least 100 yards per minute to give a ratio of spinning speedto extrusion velocity of between 2.5:1 and 4:1,

(2') The temperature of the relaxing bath must be between 0 C. and 120C., and not more than one of said critical conditions is outside of thefollowing ranges for the indicated condition:

(7') Salt index of viscose 3.5 to 5.5.

(k) Sulfuric acid content of bath 7.5% to 8.5%. (Z) Sodium sulfatecontent of bath 1- 19% to 25%. (m) Zinc sulfate content of bath 0.85% to2.0%. (11) Length of travel in bath Over 75 inches. (0) Temperature ofcoagulating bath to 60 C. (10) Temperature of relaxing bath 60 to 100 C.

It will be seen that the above process differs .from and is animprovement over the process of U. S. Patent No. 2,515,834 to Nicoll inthat heavy denier filaments (greater than 10 denier per filament) arespun at high speed (spinning speeds of at least 100 yards per minute) bymain taining a ratio of spinning speed to extrusion velocity of between2.511 and 4:1. This latter condition does not apply to the spinning ofordinary deniers. For filament deniers below 10, at spinning speeds ashigh as 100 yards per minute, extrusion velocities which are about equalto or slightly lower than the feed-wheel or spinning speed have beensatisfactory. Further lowering of the extrusion velocity to one-ha1f thespinning speed in the spinning of the fine denier filaments results inpoor spinning performance characterized by filament breaks and filamentwraps.

When spinning heavy denier material, the appropriate extrusion velocityto obtain satisfactory crimping is critically different. Unexpectedly,it has been found necessary to use a ratio of spinning speed toextrusion velocity of between about 2.5: 1

and 4:1 at spinning speeds of at least about yards per minute. Operatingat higher extrusion velocities lowers the breaking tension of thefilaments with an accompanying serious reduction in crimpability and, inaddition, also results in poor spinning performance. Reducing theextrusion velocity below the range disclosed above likewise results inpoor spinning performance, and there is no apparent increase in thecrimpability of the filaments.

The table illustrates the important aspects of the invention. Yarn of 18denier per filament was spun at a spinning speed of 100 yards per minutein accordance with the general procedure disclosed in U. S. Patent No.2,515,834, except for the changes indicated. A viscose solutioncontaining 7% cellulose and 6% alkali was spun at a sodium chlorideindex of 3.6 into a bath at a temperature of 56 C. containing 8.5%sulfuric acid, 24% sodium sulfate, 1.5% zinc sulfate, and

Table Extrusion i i fii Breaking 8 8:31 Orim Velocity, S peed t5 zggiTiension? Waves get Yds./Min. Extrusion Grams per Inch Velocity DenierThese data illustrate the necessity for reducing the extrusion velocityin order to obtain breaking tensions that will produce fibers that arecapable of crimping to a commercially useful extent. sions, of the ordernecessary to produce heavy denier fibers of commercially acceptablecrimpability, can only be obtained by substantially reducing theextrusion velocity. At this spinning speed of 100 yards per minute,satisfactory breaking tensions are obtained when extruding at velocitiesof 33 to 39 yards per minute.

Similarly when spinning yarn of 10 deniers per filament at spinningspeeds of 100 yards per minute, optimum performance, based on acomparison of the breaking tensions obtained and the number ofinterruptions due to poor spinning, resulted atan extrusion velocity of34.5 yards per minute. This extrusion velocity, which corresponds to aratio of spinning speed to extrusion velocity ratio of 2.90, resulted ina breaking tension of 0.60 g. p. d. This permitted operation at aspinning tension of 0.50 g. p. d.

When this discovery was applied to the finer, lighter yarns, it wasfound that optimum performance was obtained at lowered extrusionvelocities, but these velocities were at least 1.5 to 2 times theoptimum extrusion velocities found in the case of the heavy denieryarns. Thus, when spinning yarn of 6 deniers per filament at 100 yardsper minute optimum performance was achieved at an extrusion velocity of54 yards per minute, corresponding to a spinning speed i to extrusionvelocity ratio of 1.85. At this ratio Further, they illustrate thatbreaking tenbreaking tension of 0.87 g. p. d. and an operable spinningtension of 0.73 g. p. d.

It is apparent that the spinning of crimpable fibers of heavy denierfilaments and higher) depends on spinning at high spinning tension.Imposing a high spinning tension on heavy denier filaments necessitatesincreasing th breaking tension of the filaments. Increasing this tensionis, surprisingly, accomplished by substantially reducing the extrusionvelocity to increase the ratio of spinning speed to extrusion velocity.When spinning at a speed of 100 yards per minute, it is necessary thatthe value of this ratio be above about 2.5 to 1 and preferably not over3 to 1. If the spinning speed is increased, the range of this ratio mayalso be increased above 2.511 to values not in excess of about 4:1.

This invention provides an improved and an inexpensive method forproducing the crimped filaments and fibers which find a wide demand inindustry. This method requires no additional equipment and makes itpossible to produce a satisfactory heavy denier, crimped fiber, whichheretofore had not been possible. The method is applicable to fibersproduced by the bucket, bobbin, or any of the continuous spinningprocesses. These fibers are useful, not only for new effects intextiles, but also for other industrial applications, e. g., asartificial down or hair substitutes. Further, these filaments are usefulas a replacement for wool in carpets, rugs, and other floor coverings,and upholstery.

As many different embodiments of the present invention may be madewithout departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsdisclosed except to the extent defined in the appended claims.

What is claimed is:

1. In the process for producing crimpable regenerated cellulosefilaments and fibers wherein a viscose solution having an alkali contentof 4% to 7.5% and a salt index between 1.5 and 7 is extruded in the formof filaments into a coagulating and regenerating bath having a sul- 6yards per minute using an extrusion velocity which provides a ratio ofspinning speed to extrusion velocity of between 2.521 and 4:1.

2. A process for producing 10 to 18 denier crimped regenerated cellulosefilaments and fibers which comprises extruding a viscose, having analkali content of 4% to 7.5% and a salt index of 8.5 to 5.5, in the formof filaments at an extrusion velocity of 33 to 39 yards per minute intoa coagulating and regenerating bath having a sulfuric acid content of7.5% to 8.5%,

furic acid content between 6.5% and 9.5%, a

sodium sulfate content between 15% and 30%, a zinc sulfate contentbetween 0.1% and 3% and a temperature between 40 C. and 75 C., theresulting filaments are conducted through the bath for at least 50inches, the filaments are stretched under a tension approaching thebreaking tension and wherein not more than one of the above criticalconditions is outside of the following range for the indicatedcondition:

Salt index of viscose 3.5 to 5.5. Sulfuric acid content of bath 7.5% to8.5%. Sodium sulfate content of bath 19% to 25%. Zinc sulfate content ofbath 0.85% to 2.0%. Length of travel in bath Over 75 inches. Temperatureof coagulating bath50" to 60 C.

the improvement for obtaininga high degree of crimp when spinning heavydenier filaments which comprises spinning filaments of 10 to 18 deniersper filament at a speed of at least 100 a sodium sulfate content of 19%to 25%, a zinc sulfate content of 0.85% to 2.0% and a temperature of 50to 60 C., conducting the resulting filaments through the bath for overinches and stretching them under a tension approaching the breakingtension, withdrawing the filaments from the bath at a spinning speed ofabout yards per minute and, after substantially complete regeneration,suspending the filaments in complete absence of tension in an aqueousliquid bath at a temperature of 0 to C. until completely relaxed.

3. A process for producing 10 to 18 denier crimped regenerated cellulosefilaments and fibers which comprises extruding a viscose solution havingan alkalioontent of 4 to 7.5% and a salt index of 3.5 to 5.5 through aspinneret into a coagulating and regenerating bath having a sulfuricacid content of 7.5% to 8.5%, a sodium sulfate content of 19 to 25%, azinc sulfate content of 0.85 to 2.0% and a temperature of 50 to 60 0.,through the bath for over 75 inches and stretching them under a tensionapproaching the breaking tension, withdrawing the stretched filaments ata spinning speed of at least 100 yards per minute the extrusion velocityand size of spinneret orifices being correlated with the spinning speedto give filaments of 10 to 18 deniers per filament and a ratio ofspinning speed to ex trusion velocity of between 2.5:1 and 3:1 and,after substantially complete regeneration, suspending the filaments incomplete absence of tension in an aqueous liquid bath at a temperatureof 60 to 100 C. until completely relaxed.

4. A process for producing 10 to 18 denier crimpable regeneratedcellulose filaments and fibers which comprises extruding a viscosesolution having an alkali content of 4 to 7.5% and a salt index of 3.5to 5.5 through a spinneret into a coagulating and regenerating bathhaving a sulfuric acid content of 7.5 to 8.5%, a sodium sulfate contentof 19 to 25%, a zinc sulfate content of 0.85 to 2.0% and a temperatureof 50 to 60 C., conducting the resulting filaments through the bath forover 75 inches and stretching them under tension approaching thebreaking tension, withdrawing the stretched filaments at a spinningspeed of at least 100 yards per minute and completing the regeneration,the extrusion veloity and size of spinneret orifices being cor-References Cited in the file of this patent UNITED STATES PATENTS NameDate Nicoll July 18, 1950 Number conducting the resulting filaments,

1. IN THE PROCESS FOR PRODUCING CRIMPABLE REGENERATED CELLULOSEFILAMENTS AND FIBERS WHEREIN A VISCOSE SOLUTION HAVING AN ALKALI CONTENTOF 4% TO 7.5% AND A SALT INDEX BETWEEN 1.5 AND 7 IS EXTRUDED IN THE FORMOF FILAMENTS INTO A COAGULATING AND REGENERATING BATH HAVING A SULFURICACID CONTENT BETWEEN 6.5% AND 9.5%, A SODIUM SULFATE CONTENT BETWEEN 15%AND 30%, A ZJNC SULFATE CONTENT BETWEEN 0.1% AND 3% AND A TEMPERATUREBETWEEN 40* C. AND 75* C., THE RESULTING FILAMENTS ARE CONDUCTED THROUGHTHE BATH FOR AT LEAST 50 INCHES, THE FILAMENTS ARE STRETCHED UNDER ATENSION APPROACHING THE BREAKING TENSION AND WHEREIN NOT MORE THAN ONEOF THE ABOVE CRITICAL CONDITIONS IS OUTSIDE OF THE FOLLOWING RANGE FORTHE INDICATED CONDITION: